1. Field of the Invention
The present invention relates to an inkjet recording apparatus in which ink droplets are ejected to print.
2. Description of Related Art
An inkjet head includes a passage unit in which there are formed nozzles to eject ink droplets and pressure chambers connected to the respective nozzles; and a piezoelectric actuator to give ejection energy to ink in each pressure chamber. The piezoelectric actuator changes the volume of each pressure chamber to apply pressure to ink in the pressure chamber. In an inkjet head disclosed in Japanese Patent Unexamined Publication No. 2002-36568, a piezoelectric actuator includes a piezoelectric layer disposed over a plurality of pressure chambers; a plurality  of individual electrodes being opposed to the respective pressure chambers; and a common electrode being kept at a reference potential and opposed to the individual electrodes across the piezoelectric layer. In the piezoelectric actuator, when a voltage pulse signal is given to an individual electrode, electric field is impressed along the thickness of the piezoelectric layer to a portion of the piezoelectric layer being sandwiched by the individual electrode and the common electrode. The electric field elongates the thickness of the portion of the piezoelectric layer. Thereby, the volume of the corresponding pressure chamber is changed so that pressure is applied to ink in the pressure chamber.
In inkjet recording apparatuses, an increase in printing speed is desired. To increase printing speed, the ink ejection cycle of each nozzle must be shortened. When the ink ejection cycle is shortened, quick-drying ink must be used so that ink droplets having impacted a recording paper dry quickly. However, when such quick-drying ink is used, the viscosity of ink in each nozzle may increase by drying. This brings about deterioration of ink ejection performance or defective ejections. As a method for avoiding the above problem, So-called “ejection flushing” is known in which ink having increased in viscosity is ejected from each  nozzle toward a place other than a printing paper. However, when ejection flushing is frequently performed, a considerable amount of ink is wastefully consumed.
For the above reason, in some cases, so-called “non-ejection flushing” or “dummy flushing” is performed by driving the actuator to the extent that any nozzle does not eject an ink droplet, and thereby agitating ink in each nozzle. The width of the pulse to be given to each individual electrode in non-ejection flushing, is smaller than the width of the pulse for allowing each nozzle to eject ink droplets. In non-ejection flushing, however, it is required to increase the number of drives of the actuator in comparison with ejection flushing. This increases the power consumption of the inkjet recording apparatus.
In another non-ejection flushing method than the above-described method, each individual electrode is given a level of a voltage pulse lower than the level for allowing each nozzle to eject ink droplets. In this method, however, a voltage control circuit is required to properly control the level of the voltage pulse to one of the two levels. This increases the manufacturing cost of the inkjet recording apparatus. 